I hope I am reading this wrong, and you are not just starting to feed 6 week old pups?? If so, you better start feeding them fast, or they will eat each other! They must be starving! But to answer your question, I feed 3 or 4 times a day, depending on the litter. They get all they want each meal, and mom cleans up the rest.
I start feeding at 3 weeks so by 6 they are weaned and eating 4 meals a day. And I do know how much they are getting. Just want them all the same size so I don't free feed. Works, so why change it. Doing this for years. Some do seem to have luck with free feeding.
At around 3 weeks I put dry food in the whelping box in the corner under the pig rail and a pan of waterin another corner. They are free fed. When they are hungry they start to munch, never overeat, always look well filled out and solid.The slow eaters always get all they need.If I keep several puppies I continue to free feed until 6 mo or so.Have been doing it for years.